1. Field of the Invention
The present invention generally relates to line module protection methods and devices utilizing those methods, and, more particularly, to a method of protecting a line module in a line accommodating unit of each of the devices that constitute a network system, and an device utilizing that method.
2. Description of the Related Art
A network system shown in FIG. 1 comprises a switching device 10, a transmitting device 11, and terminal devices 12 and 13. Each of these devices is provided with line accommodating units 10a, 11a, 12a, and 13a. 
FIG. 2 shows the structure of each line accommodating unit. Normally, a pair of lines are used for communication between devices, and a line accommodating unit 14 comprises N of line accommodating modules 161 to 16N for accommodating L pairs of lines. The line accommodating modules 161 to 16N serve as an interface between a device 18 (or a xe2x80x9ccommon unitxe2x80x9d in relation to the line accommodating modules) and the lines. The line accommodating modules 161 to 16N is detachable from the line accommodating unit 14, so that the number of lines can be changed.
Where one of the line accommodating modules 161 to 16N breaks down, line module protection is performed to prevent the connection between the common unit and the accommodated lines from being cut off. As shown in FIG. 3A, the line accommodating unit 14 includes an auxiliary module 16N+1 as well as the line accommodating modules 161 to 16N (hereinafter referred to as xe2x80x9coperating modulesxe2x80x9d). The auxiliary module 16N+1 does not normally operate. However, when a failure occurs in one of the operating modules, the auxiliary module 16N+1 starts operating. For instance, if the operating module 162 breaks down, the auxiliary module 16N+1 replaces the operating module 162 to perform the line module protection, as shown in FIG. 3B. In FIGS. 3A and 3B, the number L of pairs of lines in each module is 1.
FIG. 4 shows the structure of the conventional line module protection. To perform the line module protection, a protection unit 20 is disposed between the line accommodating unit 14 and the lines. Furthermore, a switching unit 22 and a CPU 24 are disposed in the common unit 18.
The protection unit 20 is a functional block that is added to perform the line module protection. To switch lines, switches 30 disposed on the lines are controlled. Where one line is constituted by a Tip signal and a Ring signal, two switches 30 are necessary for one line, and four switches 30 for one input line and one output line are used to switch the connection between the lines and a line accommodating module.
FIG. 5 illustrates the line module protection where the operating module 162 breaks down. The CPU 24 is notified of the breakdown of the operating module 162 through a module breakdown information line F2. Based on this notification, the CPU 24 instructs the switching unit 22 to switch lines #2 from the operation module 162 to the auxiliary module 16N+1. The CPU 24 also switches a switch control signal C2 for a corresponding one of the switches 30 from the low level to the high level so as to switch the lines. As shown in FIG. 4B, when a switch control signal is low, a switch 30 connects a terminal C to a terminal A, and when the switch control signal is high, the switch 30 connects the terminal C to a terminal B.
A user is notified of the breakdown through a display 26, and is urged to exchange the operating module 162 for a new one. If the auxiliary module 16N+1 breaks down, the user is notified of the breakdown through the display 26, and is urged to exchange the auxiliary module 16N+1 for a new one, without switching the lines.
Generally, the failure rate of the switches 30 is much lower than the failure rate of the line accommodating modules. Therefore, the line module protection is performed so as to lower the failure rate of the entire line accommodating unit 14. By doing so, the failure time is also shortened.
However, in the above conventional method, the auxiliary module is located at an end in the series arrangement of the operating modules, because the auxiliary module is typically provided as a secondary addition to the primary operating modules. If an operation module breaks down more than a predetermined distance away from the auxiliary module, lines disposed between the auxiliary module and the broken operating module (this line will be hereinafter referred to as xe2x80x9cprotection signal linexe2x80x9d) may be too long to ensure proper transmission characteristics, thereby hindering proper line module protection. As a result, with the above method, a single auxiliary module cannot provide sufficient protection for as many operating modules as may be desired. Furthermore, even through some of the operating modules do not require line module protection, the protection unit is mounted as one block, resulting in an increase of the hardware costs.
A general object of the present invention is to provide line module protection methods and devices in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a line module protection method and a device utilizing that method, by which the number N of line accommodating modules for line module protection can be made greater with respect to one auxiliary module, and the hardware can be flexibly reduced in accordance with the number N of line accommodating modules.
The above objects of the present invention 5 are achieved by a line module protection method for protecting a plurality of line accommodating modules included in a line accommodating unit connected to lines that constitute a network.
This method comprises the steps of:
dividing the plurality of line accommodating modules into a plurality of groups;
switching a connection from a broken one of the plurality of line accommodating modules to an auxiliary module; and
locating the auxiliary module substantially at the same distance from all the plurality of groups.
In the above device of the present invention, the plurality of line accommodating modules are divided into the plurality of groups, and the auxiliary module is located substantially at the same distance from all the groups. Thus, the number N of line accommodating modules for line module protection can be made greater with one auxiliary module.